A method and device for improving dielectric heating uniformity based on a coating of wave-absorbing particles

Abstract

The application belongs to the field of food heating, and discloses a method for improving the uniformity of dielectric heating based on a wave-absorbing particle coating, which can uniformly heat a predetermined food stack without directly contacting the surface of the food stack, by setting the density distribution of electromagnetic wave-absorbing particle clusters corresponding to the cold and hot zone distribution of the predetermined food stack, thereby avoiding the negative impact on the original quality of the food stack and reducing the willingness of consumers to purchase. First, the accumulation shape of the predetermined food stack is obtained through simulation, and a corresponding cold and hot zone distribution model is obtained. Then, a hollow heat-conducting element is set to be inserted into the predetermined food stack, the hollow heat-conducting element contains electromagnetic wave-absorbing particle clusters, and the distribution density of the electromagnetic wave-absorbing particle clusters in the hollow heat-conducting element is set based on the cold and hot zone distribution model of the predetermined food stack, thereby realizing the uniform heating of the predetermined food stack. The application also discloses a dielectric heating uniform heating device based on a wave-absorbing particle coating, which can better implement the above method.

Description

Technical Field

[0001] This invention belongs to the field of food heating and discloses a method and apparatus for improving dielectric heating uniformity based on a microwave absorbing particle coating. Background Technology

[0002] Dielectric heating is a method of heating through microwaves and radio frequencies. It is widely used in food thawing, heating, drying, sterilization, insecticidal and enzyme inactivation. Its principle is to generate heat by causing the microscopic particles such as ions, atoms and molecules inside the food to rotate continuously under the action of an alternating electromagnetic field and rub against each other, thus achieving a rapid overall heating effect.

[0003] Dielectric heating is still affected by the dielectric properties of food and edge effects, which can still cause a certain degree of uneven heating, resulting in poor heating effect and thus affecting the application of dielectric heating technology in industry. Common methods to improve the uniformity of dielectric heating of food are mainly through adjusting the electrode plate spacing, power, changing the shape of food, adding conveyor belts, and adding heating media. However, because the dielectric loss factor of food is very low during the processing of frozen and dried foods, and it is difficult to change its geometric characteristics, the common methods of adjusting heating uniformity are difficult to use to improve the uniformity of frozen and low-moisture foods.

[0004] The reason for the poor implementation effect is that when two or more surfaces of the food intersect at a certain angle, the electric field tends to pass through each surface perpendicularly, resulting in a higher electric field strength at these intersections. This causes the heating rate at the corners to be much higher than that in the center of the food. In other words, the dielectric heating rate is different in different parts of the food, which means that there are cold and hot spots in the food during dielectric heating, making it difficult for dielectric heating to heat the food evenly.

[0005] Currently, several improvements have been made to dielectric heating in this regard. Specifically, micro / nano metal powders with large specific surface area and small size are used as thermally conductive particles to enhance the heating efficiency of dielectric heating. For example, immersing frozen sea bream in a CS@Fe3O4 solution can improve the temperature distribution uniformity of microwave-thawed fish fillets. Another example is using magnetic nanoparticles to embed low-temperature biological tissues, which improves the heating rate and temperature distribution uniformity of samples during microwave reheating.

[0006] However, although the improved implementation method enhances the heating uniformity of dielectric heating, the direct contact between food and micro / nano metal powder may negatively affect the original quality of the food and reduce consumers' willingness to buy. Moreover, this implementation method cannot accurately locate the cold zone in the food, resulting in poor heating uniformity. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method and apparatus for improving dielectric heating uniformity based on a microwave absorbing particle coating. This method can heat food uniformly through electromagnetic wave absorbing particle clusters without direct contact with the food surface, thereby avoiding negative impacts on the original quality of the food and reducing consumers' willingness to purchase.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for improving dielectric heating uniformity based on a microwave absorbing particle coating, used for uniformly heating a predetermined food pile, characterized by comprising the following steps:

[0010] Step S1: Obtain the stacking shape of the predetermined food pile and the corresponding cold and hot zone distribution model through simulation;

[0011] Step S2: Set a hollow heat-conducting component to be inserted into the predetermined food pile. The hollow heat-conducting component contains electromagnetic wave absorbing particle clusters. Based on the cold and hot zone distribution model of the predetermined food pile, set the distribution density of electromagnetic wave absorbing particle clusters in the hollow heat-conducting component to achieve uniform heating of the predetermined food pile.

[0012] Preferably, in step S2: the distribution density of electromagnetic wave absorbing particle clusters in the hollow heat-conducting component corresponding to the cold zone of the predetermined food pile is greater than the distribution density of electromagnetic wave absorbing particle clusters in the hollow heat-conducting component corresponding to the hot zone of the predetermined food pile, so that the heating rate of the cold zone of the predetermined food pile is greater than the heating rate of the hot zone of the predetermined food pile.

[0013] Preferably, the electromagnetic wave absorbing particle cluster is formed by the aggregation of multiple electromagnetic wave absorbing particles, which are magnetic metal oxide particles or magnetic metal particles.

[0014] Furthermore, the particle size of the electromagnetic wave absorbing particles ranges from 20 nm to 20 μm, and the saturation magnetization is greater than 50 emu / g.

[0015] Preferably, the hollow thermally conductive component is made of a non-metallic material with a dielectric constant of less than 9, a dielectric loss of less than 0.05, and a thermal conductivity of greater than 20 W / mK. Furthermore, the electromagnetic wave absorbing particle cluster is formed by the adsorption and aggregation of multiple electromagnetic wave absorbing particles on the inner wall of the hollow thermally conductive component through thermal spraying or electrostatic printing.

[0016] Preferably, the food is stacked in a predetermined heating container and heated by a cluster of electromagnetic wave-absorbing particles, and the dielectric constant of the material of the predetermined heating container is less than 9 and the dielectric loss is less than 0.05.

[0017] A uniform heating device based on dielectric heating is characterized in that it includes a heating container, which is the heating container described above; an electromagnetic wave generating component for generating high-frequency electromagnetic waves in the heating container; and a hollow heat-conducting component, which is the hollow heat-conducting component described above, disposed on the inner wall of the heating container.

[0018] Preferably, the present invention further includes a movable guide frame disposed on the inner side wall of the heating container. The movable guide frame has a movable guide rod parallel to the inner side wall, and one end of the hollow heat-conducting component has a guide groove that corresponds to and cooperates with the movable guide rod, so that the hollow heat-conducting component is movably disposed on the inner wall of the heating container.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. The method for improving dielectric heating uniformity based on microwave absorbing particle coating of the present invention firstly obtains the stacking shape of a predetermined food pile and the corresponding cold and hot zone distribution model through simulation; then, a hollow heat-conducting component is inserted into the predetermined food pile, the hollow heat-conducting component containing electromagnetic wave absorbing particle clusters, and the distribution density of electromagnetic wave absorbing particle clusters in the hollow heat-conducting component is set based on the cold and hot zone distribution model of the predetermined food pile, thereby achieving uniform heating of the predetermined food pile. Therefore, the present invention can achieve uniform heating of the predetermined food pile without direct contact with the food surface by setting the density distribution of electromagnetic wave absorbing particle clusters corresponding to the cold and hot zone distribution of the predetermined food pile, and avoids reducing consumers' willingness to purchase due to negative impact on the original quality of the food.

[0021] 2. Because the distribution density of electromagnetic wave absorbing particle clusters in the hollow heat-conducting component corresponding to the cold zone of the predetermined food pile is greater than that in the hollow heat-conducting component corresponding to the hot zone of the predetermined food pile, the heating rate of the cold zone of the predetermined food pile is greater than that of the hot zone. Therefore, by setting electromagnetic wave absorbing particle clusters with a higher density in the cold zone of the predetermined food pile, the cold zone of the predetermined food pile receives more heating heat than the hot zone, and the heating rate of the cold zone of the predetermined food pile is greater than that of the hot zone, thereby further achieving uniform heating of the predetermined food pile more quickly.

[0022] 3. Because the heating device for improving dielectric heating uniformity based on absorbing particle coating of the present invention includes a heating container, an electromagnetic wave generating component and a hollow heat-conducting component, and the electromagnetic wave generating component is used to generate high-frequency electromagnetic waves in the heating container, the uniform heating device based on dielectric heating of the present invention can better implement the method of improving dielectric heating uniformity based on absorbing particle coating. Attached Figure Description

[0023] Figure 1This is a schematic diagram of the steps of a method for improving dielectric heating uniformity based on a microwave absorbing particle coating according to Embodiment 1 of the present invention;

[0024] Figure 2(a) is a schematic diagram of the cold spot distribution of the cylindrical spatial shape formed by the natural accumulation of food piles according to the present invention;

[0025] Figure 2(b) is a schematic diagram of the cold spot distribution image of the rectangular spatial shape formed by the natural accumulation of food piles according to the present invention;

[0026] Figure 2(c) is a schematic diagram of the cold spot distribution image of the cone-shaped spatial shape formed by the natural accumulation of food piles according to the present invention;

[0027] Figure 3 This is a schematic diagram of a uniform heating device based on dielectric heating according to Embodiment 1 of the present invention;

[0028] Figure 4 This is a schematic diagram of the heating container according to Embodiment 1 of the present invention; and

[0029] Figure 5 This is a schematic diagram of the heating container and the movable guide frame according to Embodiment 2 of the present invention.

[0030] In the figure: S100, Method for improving dielectric heating uniformity based on microwave absorbing particle coating; 100, Heating device for improving dielectric heating uniformity based on microwave absorbing particle coating; 10, Heating container; 11, Heat-conducting component slot; 12, Fixing clamp; 121, Set screw; 20, Moving guide frame; 21, Moving guide rod; 30, Electromagnetic wave generating assembly; 31, Radio frequency generator; 32, Electrode plate; 40, Hollow heat-conducting component; 50, Temperature sensor. Detailed Implementation

[0031] To make the technical means, creative features, objectives and effects of the present invention easier to understand, the following embodiments, in conjunction with the accompanying drawings, specifically illustrate the method and apparatus for improving dielectric heating uniformity based on microwave absorbing particle coating of the present invention. It should be noted that the description of these embodiments is for the purpose of helping to understand the present invention, but does not constitute a limitation of the present invention.

[0032] <Example 1>

[0033] like Figure 1 As shown, the method S100 for improving dielectric heating uniformity based on a microwave absorbing particle coating in this embodiment is used to uniformly heat a predetermined food pile, and is characterized by including the following steps:

[0034] Step S1: Obtain the stacking shape of the predetermined food pile and the corresponding cold and hot zone distribution model through simulation.

[0035] Specifically, in this field, based on common knowledge derived from a large amount of experimental data, a predetermined food pile consists of multiple predetermined foods. The predetermined foods have edges, corners, and a textured surface formed by the enclosed edges and corners. When the predetermined food pile is dielectrically heated, the edges, corners, and edges of the predetermined foods heat up faster, i.e., they are heated more quickly. As a result, the heating rate of the predetermined food pile as a whole is uneven, leading to a non-uniform spatial distribution of cold and hot zones in the heated predetermined food pile. The distribution of cold and hot zones in the predetermined food pile corresponding to the predetermined stacking shape of the predetermined foods is relatively constant.

[0036] Specifically, the cold and hot zone distribution model, i.e. the distribution image, is obtained by simulation program for the various spatial shapes formed by the natural accumulation of the predetermined food pile. In this embodiment, the predetermined food is a unit whole of fish, shrimp and grain.

[0037] In this embodiment, the hot and cold zone distribution model is as follows:

[0038]

[0039] The food is placed in a predetermined heating container and heated by a cluster of electromagnetic wave absorbing particles. The material of the predetermined heating container has a dielectric constant of less than 9 and a dielectric loss of less than 0.05. The electromagnetic wave absorbing particles are micro-nano metal powders of dielectric loss absorbing materials. Micro-nano metal powders have a large specific surface area and small size, making them good absorbers and heat conductors. The dielectric loss absorbing materials mainly include various carbon materials, polymers, and perovskite oxides. Materials with magnetic loss as the main component include ferrites (CoFe2SO4, MnFe2O4, ZnFe2O4, etc.), magnetic metal oxides (Fe3O4, γ-Fe2O3, CoO, etc.), and magnetic metals (Fe, Co, Ni and their alloys). Specifically, the electromagnetic wave absorbing particles are selected from one or more of the following: carbon black, graphite, silicon carbide, barium titanate, silicon nitride, metals (iron, cobalt, nickel) and their oxides, and carbon / magnetic composite particles.

[0040] Step S2: Set a hollow heat-conducting component to be inserted into the predetermined food pile. The hollow heat-conducting component contains electromagnetic wave absorbing particle clusters. Based on the cold and hot zone distribution model of the predetermined food pile, set the distribution density of electromagnetic wave absorbing particle clusters in the hollow heat-conducting component to achieve uniform heating of the predetermined food pile.

[0041] The distribution density of electromagnetic wave absorbing particle clusters in the hollow heat-conducting component corresponding to the cold zone of the predetermined food pile is greater than that in the hollow heat-conducting component corresponding to the hot zone of the predetermined food pile, thus the heating rate of the cold zone of the predetermined food pile is greater than that of the hot zone of the predetermined food pile.

[0042] The food is stacked in a predetermined heating container and heated by a cluster of electromagnetic wave-absorbing particles. The material of the predetermined heating container has a dielectric constant of less than 9 and a dielectric loss of less than 0.05.

[0043] Specifically, the hollow thermal conductive component is made of non-metallic material with a dielectric constant of less than 9, a dielectric loss of less than 0.05, and a thermal conductivity of greater than 20 W / mK. Furthermore, the electromagnetic wave absorbing particle cluster is formed by multiple electromagnetic wave absorbing particles adsorbing and aggregating on the inner wall of the hollow thermal conductive component through thermal spraying or electrostatic printing, thereby allowing the distribution density of electromagnetic wave absorbing particle clusters at different positions on the inner wall to be adjusted as needed.

[0044] Specifically, the electromagnetic wave absorbing particle cluster is formed by the aggregation of multiple electromagnetic wave absorbing particles. The electromagnetic wave absorbing particles are magnetic metal oxide particles or magnetic metal particles. The particle size of the electromagnetic wave absorbing particles ranges from 20nm to 20μm, and the saturation magnetization is greater than 50 emu / g. Specifically, the particle density of the electromagnetic wave absorbing particle cluster in the hollow heat-conducting component can be adjusted within a range according to different expected heating efficiency and uniformity. In this embodiment, the electromagnetic wave absorbing particles are iron oxide particles, which are heated in a radio frequency field for 5 minutes, and their temperature rises from 25 degrees Celsius to 40 degrees Celsius.

[0045] like Figure 3 As shown, the heating device 100 for improving dielectric heating uniformity based on the absorbing particle coating is used to implement the above-mentioned method S100 for improving dielectric heating uniformity based on the absorbing particle coating. It includes a heating container 10, an electromagnetic wave generating component 30, and a hollow heat-conducting component 40.

[0046] like Figure 4 As shown, the heating container 10 is the heating container described in the above-mentioned method S100 for improving dielectric heating uniformity based on microwave absorbing particle coating. In this embodiment, the heating container 10 is a rectangular body made of polypropylene.

[0047] The electromagnetic wave generating assembly 30 is used to generate radio frequency electromagnetic waves in the heating container 10. Specifically, the electromagnetic wave generating assembly 30 includes a flat-plate radio frequency heater consisting of a radio frequency generator 31 and a pair of electrode plates 32. The heating container 10 is located between the pair of electrode plates 32, so that the flat-plate radio frequency heater heats the heating container 10.

[0048] The hollow heat-conducting component 40 is the hollow heat-conducting component described in the above-mentioned method S100 for improving dielectric heating uniformity based on a wave-absorbing particle coating. The hollow heat-conducting component 40 is disposed on the inner wall of the heating container 10. Specifically, the hollow heat-conducting component 40 is a hollow long tube. The inner surface of the hollow heat-conducting component 40 is coated with a layer of iron oxide particles. The aggregated iron oxide particles are called electromagnetic wave absorbing particle clusters. In this embodiment, the inner surface of the hollow heat-conducting component 40 is formed into electromagnetic wave absorbing particle clusters with uneven density by electrostatic printing based on the cold and hot zone distribution of a predetermined food pile.

[0049] The inner side wall of the heating container 10 has a heat-conducting component slot 11 and a fixing clamp 12. Specifically, the end of the hollow heat-conducting component 40 is inserted into the heat-conducting component slot 11. The fixing clamp 12 is fixed on the inner wall surface of the heating container 10 and is located at the opening of the heat-conducting component slot 11, extending along the edge of the opening. The fixing clamp 12 has a set screw 121 that can be screwed into the heat-conducting component slot 11. In this embodiment, the heat-conducting component slot 11 is a cylindrical blind hole, and the fixing clamp 12 is a semi-circular clamp. The heat-conducting component slots 11 are located on opposite inner side walls of the heating container 10 and are in corresponding positions.

[0050] One end of the hollow heat-conducting element 40 is inserted into the heat-conducting element slot 11, thereby the hollow heat-conducting element 40 is detachably mounted on the inner wall of the heating container 10. Specifically, after the end of the hollow heat-conducting element 40 is inserted into the heat-conducting element slot 11, the set screw 121 is screwed in and pressed against the circumferential surface of the hollow heat-conducting element 40, thereby fixing the hollow heat-conducting element 40 relative to the heating container. In this embodiment, both ends of the hollow heat-conducting element 40 are respectively clamped inside the heating container 10 by the fixing clamps 12 at both ends.

[0051] In this embodiment, the uniform heating device 100 based on dielectric heating further includes a temperature sensor 50 for detecting the internal temperature of the heating container 10, and the temperature sensor 50 is located outside the electromagnetic wave generating component 30.

[0052] The application of the dielectric heating-based uniform heating device 100 will be illustrated below with comparative examples:

[0053] Equal batches of Litopenaeus vannamei chunks were individually frozen to -18°C and then subjected to different heating methods, including this embodiment. The comparison results are shown in the table below:

[0054]

[0055] The table above shows that, compared to Comparative Examples 1 and 2, the application of this embodiment to thaw the predetermined food pile not only requires a shorter thawing time, but also significantly reduces the maximum temperature difference between the hot and cold zones, meaning that the heating uniformity of the predetermined food pile is significantly improved.

[0056] In this embodiment, the heating container 10 is a 285×190×80mm3 cuboid polypropylene container, which has 5 hollow heat-conducting components 40 fixed inside, and the inner wall of the hollow heat-conducting components 40 is coated with a layer of iron oxide powder (20μm).

[0057] <Example 2>

[0058] In this second embodiment, the same symbols are used for the same structures as in the first embodiment, and the same descriptions are omitted.

[0059] In Embodiment 2, the structure of the uniform heating device 100 based on dielectric heating differs from that in Embodiment 1 in that:

[0060] It includes the movable guide frame 20, but excludes the heat-conducting slot 11 and the fixing clamp 12 of Embodiment 1.

[0061] like Figure 5 As shown, the movable guide frame 20 is disposed on the inner side wall of the heating container 10, and the movable guide frame 20 has a movable guide rod 21 parallel to the inner side wall of the heating container 10.

[0062] One end of the hollow heat-conducting component 40 has a guide groove that corresponds to and cooperates with the movable guide rod 21 (in the attached figure).

[0063] (not shown), thus the hollow heat-conducting element 40 is movably disposed on the inner wall of the heating container 10.

[0064] In this embodiment, the movable guide frame 20 is a rectangular closed frame with its long side fixed to the inner wall of the heating container 10 and its short side perpendicular to the inner wall of the heating container 10. The guide groove is a slot formed by the bent rib at the end of the hollow heat-conducting component 40, and the guide groove is engaged with the long side of the movable guide frame 20, so that the hollow heat-conducting component 40 is movable and detachable relative to the heating container 10.

[0065] The application of the dielectric heating-based uniform heating device 100 will be illustrated below with comparative examples:

[0066] Equal batches of rice were subjected to different heating methods, including this embodiment, and the comparison results are shown in the table below:

[0067]

[0068] The table above shows that, compared to Comparative Examples 1 and 2, applying this embodiment to heat the predetermined food pile not only requires a shorter heating time, but also significantly reduces the maximum temperature difference between the hot and cold zones, meaning that the heating uniformity of the predetermined food pile is significantly improved.

[0069] The above embodiments are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Various modifications or variations that can be made by those skilled in the art without creative effort within the scope of the appended claims are still within the scope of protection of this patent.

Claims

1. A method for improving the uniformity of dielectric heating based on a coating of wave-absorbing particles, for uniformly heating a predetermined food stack, characterized in that, The method comprises the following steps: Step S1: obtaining the accumulation shape of the predetermined food stack and the corresponding cold and hot area distribution model through simulation; Step S2: setting a hollow heat-conducting member inserted into the predetermined food stack, the hollow heat-conducting member containing clusters of electromagnetic wave absorbing particles, and setting the distribution density of the clusters of electromagnetic wave absorbing particles in the hollow heat-conducting member based on the cold and hot area distribution model of the predetermined food stack, so as to achieve uniform heating of the predetermined food stack, In step S2: The distribution density of the clusters of electromagnetic wave absorbing particles in the hollow heat-conducting member corresponding to the cold area of the predetermined food stack is greater than the distribution density of the clusters of electromagnetic wave absorbing particles in the hollow heat-conducting member corresponding to the hot area of the predetermined food stack, so that the heating speed of the cold area of the predetermined food stack is greater than the heating speed of the hot area of the predetermined food stack.

2. The method for improving dielectric heating uniformity based on wave-absorbing particle coating according to claim 1, wherein: wherein The clusters of electromagnetic wave absorbing particles are formed by aggregation of a plurality of electromagnetic wave absorbing particles, and the electromagnetic wave absorbing particles are magnetic metal oxide particles or magnetic metal particles.

3. The method for improving dielectric heating uniformity based on wave-absorbing particle coating according to claim 2, wherein: wherein The electromagnetic wave absorbing particles have a particle size range of 20 nm to 20 μm and a saturation magnetization greater than 50 emu / g.

4. The method for improving dielectric heating uniformity based on wave-absorbing particle coating according to claim 1, wherein: wherein, The hollow heat-conducting member is made of a non-metal material, has a dielectric constant less than 9, a dielectric loss less than 0.05, and a thermal conductivity greater than 20 W / mK, and the clusters of electromagnetic wave absorbing particles are formed by thermal spraying or electrostatic printing of a plurality of electromagnetic wave absorbing particles on the inner wall of the hollow heat-conducting member.

5. The method for improving dielectric heating uniformity based on wave-absorbing particle coating according to claim 1, wherein: wherein The predetermined food stack is placed in a predetermined heating container and heated by the clusters of electromagnetic wave absorbing particles, and the material of the predetermined heating container has a dielectric constant less than 9 and a dielectric loss less than 0.

05.

6. A dielectric heating uniform heating device based on a coating of wave-absorbing particles, characterized in that, The method comprises: a heating container, which is the heating container of claim 5; an electromagnetic wave generating assembly for generating high-frequency electromagnetic waves in the heating container; a hollow heat-conducting member, which is the hollow heat-conducting member of any one of claims 1-5, and is arranged on the inner wall of the heating container.

7. The device according to claim 6, wherein the device is a device for improving dielectric heating uniformity by using a coating of wave-absorbing particles. The method further comprises: a moving guide frame arranged on the side inner wall of the heating container, the moving guide frame having a moving guide rod parallel to the side inner wall, one end of the hollow heat-conducting member has a guide groove portion corresponding to the moving guide rod, so that the hollow heat-conducting member is movably arranged on the inner wall of the heating container.

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